The present invention relates to a coating film (hereinafter also referred to as xe2x80x9can organic thin filmxe2x80x9d), and a method and an apparatus for producing the same, in which a compound having a hydrolyzable group, e.g. a silane-based compound, is chemically bonded to a surface of a substrate.
Traditionally, methods of forming organic thin films have been developed. Typical examples of conventional technologies for forming organic thin films are bar coating, dipping, etc. According to these methods, a film having a thickness on the order of at least tens of micrometer is formed. Furthermore, these methods control the thickness of the film on the order of about micrometer, and are not suitable for controlling the film thickness on the order of nanometer. Spin coating is an example of a more controllable method than these methods, and is often used to form devices having a minute structure such as semiconductors. According to this method, formation of a film having a thickness of about one to several micrometers can be realized, and also the thickness of the film can be controlled easily. However, because the organic thin film produced by this method is not bonded integrally to a substrate, the film may peel off easily. In the manufacture of semiconductor devices, such an ease of peeling is required, and this method is utilized.
On the other hand, it already has been proposed to form a molecular film by applying a chlorosilane-based compound, which has a chlorosilyl group at an end of a molecule containing an alkyl group or a fluoroalkyl group, to a surface of glass or the like having an active hydrogen on the surface, and covalently bonding it to the surface by a hydrogen chloride elimination reaction.
As conventional technologies, there are methods in which a substrate is immersed in a coating solution containing a chlorosilane-based compound (JP 1-70917A, EP 0492545A). In another example, a method in which a chlorosilane-based compound as a gas is brought into contact with a surface of a substrate and reacted has been proposed. Also, when using an alkoxysilane-based compound, a method in which an aqueous solution thereof is prepared and hydrolyzed to form a coating film has been proposed (Research Report of Tokyo Metropolitan Industrial Center, No. 22, pages 57-60 (1993)). Furthermore, a more specific example is a method in which a molecular film is formed by roll coating (JP 10-180179 A).
The conventional immersion method is excellent when the shape of the object to be coated is not flat but is irregular. In this case, a film can be formed on the irregular surface, as a liquid reacts along the surface. However, in the immersion method, a large amount of liquid is required for immersion, and manipulations for removing and inserting a substrate are necessary. Thus, the operation becomes complex and requires a large amount of time, resulting in a high cost. Furthermore, because a chlorosilane-based compound reacts with water easily, its short pot life is a problem. Moreover, in the immersion method, because the chlorosilane-based compound is brought into contact with the entire substrate and reacted, the method is inconvenient when the substrate has a surface which is not desirable to be coated with the chlorosilane-based compound.
Furthermore, in the method in which a chlorosilane-based compound as a gas is brought into contact with a surface of a substrate and reacted, it is difficult to form a uniform molecular film. The same problem also occurs when using an alkoxysilane-based compound or an isocyanate silane-based compound. Furthermore, when using an aqueous solution of an alkoxysilane-based compound, film thickness is increased, and irregularity in film thickness is generated easily. The same applies to the case when using an isocyanate silane-based compound.
More specifically, the method in which a film is formed by roll coating has solved conventional problems in the immersion method, such as amount of liquid, complex operation, long operational time, dealing with a surface not needed to be coated, etc. However, it has a problem in that the object to be coated must be a flat plate. Moreover, there has not been any method in which an organic thin film having a thickness on the order of not more than submicrometer is produced at a low cost.
In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide a coating film and a method and an apparatus for producing the same, in which an amount of a liquid required for forming a film is decreased even when an object (substrate) to be coated with the film is not a flat plate but has an irregular shape and a large size; it is not necessary to be concerned over the pot life of a coating solution; the substrate is manipulated easily; and cost is low.
In order to accomplish the above-mentioned object, the present invention provides a first method for producing a coating film using a compound (1) represented by a general formula (1) ABXn (where A is a carbon-containing group; B is at least one element selected from Si, Ge, Sn, Ti and Zr; X is a hydrolyzable group; and n is 1, 2 or 3) as a raw material, comprising: measuring the compound (1) in an amount required for one time application (a required amount) on a surface of a substrate having an active hydrogen on the surface, and supplying it to the surface of the substrate at each time of application; in an atmosphere having a water vapor concentration of more than 0.0076 kg/m3, bringing the compound (1) into contact with the surface of the substrate, causing an elimination reaction between the active hydrogen on the surface of the substrate and the hydrolyzable group in parts of the molecules of the compound (1), thereby covalently bonding the parts of the molecules of the compound (1) to the surface of the substrate, as well as polymerizing parts of the molecules of the compound (1) with one another using water molecules present in the atmosphere.
Next, the present invention provides a second method for producing a coating film, comprising: applying a coating solution containing a silane-based compound having at least one reactive group selected from at least halogen atoms, an alkoxyl group and an isocyanate group to a surface of a substrate having an active hydrogen on the surface; causing an elimination reaction between the active hydrogen on the surface of the substrate and the reactive group of the silane-based compound, thereby covalently bonding the silane-based compound to the surface of the substrate, wherein the method comprises: conveying the substrate into a chamber in which a water vapor concentration in an atmosphere is maintained at more than 0.0076 kg/m3; measuring a coating solution containing the silane-based compound and at least one solvent not having an active hydrogen in an amount required for one time application (a required amount), and supplying it to a coating device present in the chamber at each time of application; spreading and rubbing the coating solution uniformly on the surface of the substrate with the coating device; then changing the atmosphere in the chamber and increasing a concentration of the silane-based compound, thereby accelerating an elimination reaction between the reactive group in parts of the molecules of the silane-based compound and the active hydrogen on the surface of the substrate, thereby covalently bonding the silane-based compound to the surface of the substrate; then removing the solvent, as well as polymerizing parts of the molecules of the silane-based compound with one another using water molecules present in the atmosphere.
Next, an apparatus for producing a coating film of the present invention comprises: a device for transporting a substrate from an inlet to an outlet in a chamber; a device for measuring a coating solution containing a silane-based compound and at least one solvent not having an active hydrogen in an amount required for one time application (a required amount) and supplying it to a coating device present in the chamber at each time of application; a coating device for applying and spreading the coating solution uniformly, and for accelerating an elimination reaction between the reactive group of the silane-based compound in an amount required for one time application and the active hydrogen on the surface of the substrate; a device for controlling and maintaining a water vapor concentration in an atmosphere in the chamber; and a device for removing the solvent in the coating solution.
Next, a coating film of the present invention is characterized in that: the film is transparent; the film has a thickness of 1 nm to 0.5 xcexcm; the film has a durability of at least five times for an abrasion resistance test in which a mixture of sugar and soy source (1:1 by weight ratio) is applied, heated at a high temperature of 300xc2x0 C. for 20 minutes, and cooled, then a fouling baked and adhered to the film can be removed by rubbing with a wet cloth by one""s hand; parts of the molecules of the film are covalently bonded to a surface of a substrate via at least one element selected from Si, Ge, Sn, Ti and Zr; and parts of the molecules of the film are polymerized with one another.